Drawing device



May 6, 1941,

E. G. SEASTROM DRAWING DEVICE Filed May 3, 1940 V 2 Sheds-Sheet 1 tNVENTOR (ATTORNEY Patented May 6, 1941 UNITED STATES PATENT OFFICE 2,240,719 6 DRAWING DEVICE Erik G. Seastrom, Easton, Pa. v Application May 3, 1940, Serial No. 333,185

(or. 3340) I 3 Claims.

The present invention relates to a device, and method of application of the same, for drawing ellipses, and is designed to facilitate and simplify present drafting room practices employed in drawing relatively small ellipses.

An object of the invention is the provision of a simple, inexpensive device which may be quickly and easily adjusted to describe an ellipse, more particularly an ellipse smaller than may be conveniently made by the ellipsographs now available.

Another object is the provision of a device of this character which requires no special skill to manipulate or extensive training to comprehend the principles of operation thereof.

The method of operating the device is also a feature of the invention inasmuch as it depends upon utilizing general data external to the device in making the necessary adjustments thereof, and manipulating certain elements in a manner based on specific data for describing a given ellipse. 7

Other objects of the invention will be appreciated from the following description.

Referring to the accompanying drawings;

Fig. 1 is partly a diagrammatic and partly an elevational view of a device embodying my invention;

Fig. 2 is an enlarged fragmentary sectional view of one of the arm members of the device, showing the focal hole and contiguous area laterally cut away;

Fig. 3 is a modification of the device shown in Fig. 1;

Fig. 4 is a side elevation of Fig. 3;

Fig. 5 is an enlarged fragmentary elevation of the string fastening member, and

Fig. 6 is a sectional view of Fig. 5 taken on the line 6-6 thereof.

In the drawings, Figs. 1 and 2 illustrate a simple form of a device embodying my invention, which comprises a pair of arm members I and 2 pivoted at one end in any suitable manner as for example by a disk 3 overlying the pivotal area of the arm members I and 2, and held in place by a pivotal rivet 4. The adjacent edges of the arm members I and 2 may be cut away laterally substantially one-half of their thickness so that when the ends are overlapped, they fit flush with the body surfaces of the arm members and lie in the same plane therewith. To permit the opening and closing of the arm members I and 2 about their pivotal point formed by the rivet 4, the abutting edges of the ends are made circular on a radius having the rivet 4 as its center and large enough to afford satisfactory pivotal action of the arms I and 2 about the rivet 4, The circular portions of the arm members I and 2 may terminate in shoulders 5 and 6 respectively, which when in abutting engagement limit the distance the arm members may be spread or separated at their free ends. (See Fig. 3.)

The arm members are preferably made of some plastic material which is transparent or translucent and reasonably flexible, such as Celluloid. The transparency of the material aids in using the device as will be apparent hereinafter, and the fact that the material is plastic makes it non-shatterable.

Nearthe top of each of the arm members I and 2 are located what may be termed focal holes I, and the underneath or lower surface of the arm members, contiguous to the holes 1, is laterally cut away to a depth slightly in excess of the thickness of the string 8 employed in describing the ellipse, thus forming an off-set portion 9 which permits the free movement of the string 8 when the device is in operation.

Preferably in alignment with the holes I are a series of spaced holes I0 through which the ends of the string 8 are laced, which serves as a ready means for adjusting and retaining the string in an adjusted position. To accommodate the string and permit it to lie fiush with the drawing surface, grooves or recesses II are provided, said recesses joining adjacent holes.

Referring to the modification shown in Figs. 3 to 6, which is a more refined construction of my device, it will be noted that I have provided disk members I3 which are secured to the arm members I and 2 by hollow rivets I4, the latter having a flange portion I5 at one end and spun over to form a bead I6 at the other or top end. The flange I5 is seated in a suitable recess so as to have the bottom of the rivet I4 flush with the surface of the arm members and the bead I6 does not extend all the way down, but just sufficient to retain the disk in place. I have found it expedient to have the disk I3 slightly dished, so that the periphery thereof permit the ready winding of the ends of the string 8 on the spool formed by the adjacent surfaces of the arm members and disks with the rivet I4 as the cylinder portion.

By inserting a rubber cylinder or plug I! in the center or hollow portion of the rivet I l and allowing the top end of the plug II to project slightly from the rivet I l, friction means are provided for holding the device on the drawing sur face and also affording a convenient rest for the fingers in the use of the device. This arrangement greatly facilitates retaining the device in proper position when the arms I and 2 are spread a considerable distance apart.

In this modification of my device it will be noted that the disk 3 has a lug or car formed on one side which serves as a means for cementing the disk to the arm I, and the rivet 4 secures the arm 2 to the disk 3. In this form of construction the disk functions as a bridge piece for pivotally connecting the arm members i and 2 and there is no necessity of having the abutting edges overlap as contemplated in the form shown in Figs. 1 and 2. It may also be noted it is undesirable to have too much friction at the pivotal point of the arm members I and 2 because in such a case there is'a tendency of the string to be placed under tension while setting the arm member, which operation Will be explained presently.

The operation of the device is as follows. Referring to Fig. 1 the arms I and '2 are spread apart a distance between the focal holes I, which distance is equal to the major axis of a given ellipse which it isdesired to describe. The string 8 is then pulled taut and it is held to this adjusted length, either because of the friction afforded by the holes in, or the disk members 13. After the length of the string is thus adjusted the arm members I and 2 are moved toward each other until the focal holes I coincide with the focal points of the ellipse, no further adjustment of the string being made. This partial closure of the arm members I and-2 provides a bight in the string 8 and the point of the pencil is now held perpendicular to the drawing surface and in contact with the string. Starting with the pencilpoint on the major axis and the string 8 maintained taut by the pencil point being kept in constant contact therewith, an arc is'described as the pencil point moves'off of the major axis and continues its movement until returning to the major axis on the opposite end of the curve thus described, which will be found is half of the desired ellipse. It will be understood that the minor axis of the ellipse is determined by the location of the focal points or vice. versa, and when the pencil point coincides with the minor axis the sides of string 8 form an isosceles triangle with the apex at the bight and .the legs terminating in the focal holes I; the legs being equal to half the major axis.

It is obvious that the other half of the ellipse is described in a similar manner by reversing the location of the device with respect to the initial or starting position, i. e. eith r above or below the major axis as the case may be.

The transparency of the arm members I and 2 greatly facilitates locating the focal holes 1 at thedesired point along the major axis. Further, frictionally attaching the ends of the string 8 permits easy'and accurate adjustment of the ertures, a string having its ends laced in said apertures and capable of adjustment as to the length of the bight, and the free extremity of each of the arm members having the lower sur- 7 face thereof cut away to a depth appreciably arm members.

greater than the thickness of the string and each of the end apertures extending into the cut away portions, whereby the ends of the bight have unrestricted movement about the foremost aperture of each arm member when the device is held against the drawin paper.

2. A drawing device comprising a pair of arm members pivotally secured to each other at one end and adjustable at their free ends with respect to the space therebetween, a transverse aperture formed near the free end of each of said arm members, a string threaded through said apertures, the respective ends of said string being secured to a spool member carried by each of said arm members, including a disk member secured to the several arm members by a hollow rivet forming the cylinder portion of each of the spools, the disk members forming one head of the spool members and the adjacent surfaces of the arm members serving as the other heads of the spool members, the cylinder portions of the spools being relatively short and having inserted therein rubber plugs which project slight- 1y therefrom on the lower surface of the arm member.

3. A drawing device comprising a pair of trans parent arm members pivotally secured to each other at one end and frictionally adjustable With respect to the space therebetween, a focal aperture formed near the free end of each of said arm members, a string threaded through said apertures, the respective ends of said string being. wound around a spool member carried by each of said arm members, including a disk member dished outwardly and secured to the several arm members by a hollow rivet forming the cylinder portion of the several spools, the disk members forming one head of the spool members, and the adjacent surfaces of the arm members serving as the other heads of the spools, the cylinder portions of the spools being relatively short and having an eyelet formed on one end and a flange on the other end to provide engaging means for attaching the disks to the ERIK G. SEASTROM. 

